The Stovebolt Site Forums The Shop Area Engine Shop Engine quits at high speed

I have a 1954 half ton with a 235 that has dual Rochesters through a Fenton dual intake manifold. When I'm travelling at any speed over 45 mph, the engine starts missing as if it's not getting enough gas or intermittant spark. When this happens, the engine will quit and after sitting for a minute, I can start it and drive it just fine; so long as I don't go over 45 mph. There's no vacuum leaks and the fuel pump seems to be working alright. I had a Pertronix ignition system and changed it back to the points to see if that was the problem. The problem still persists. Any ideas as to what the problem could be?

I'd wonder if the fuel pump [stock mechanical?] just can't keep up with the dual carbs above a certain flow

Bill

I had a similar problem 2 weeks ago. I replaced the coil,it got better.However, it continued so I replaced the fuel pump ,the fuel filter was good, now it runs excellent.Same problem ,I don't know, but that was mine.
Lothar

It does sound like a fuel delivery problem. Check any filters & flex hoses, or kinked tubes. Blow air back through the lines & pull the pickup tube from the tank. Some of those had a shutoff cock under the tank that can get pluged up.

I have dual rochesters with a stock pump and no fuel starve issues even at WOT. I bet wrenchbender has it nailed with crud in the tank petcock. That shutoff valve is threaded into the bottom of the tank (1/8" npt). Be careful removing it.

Curt B.

I put on a new fuel pump with the glass bowl about a year ago. The glass bowl seems full and I've cleaned it out the other day. I don't have any other fuel filters between the fuel pump and the carbs. I put in a new pickup tube with the screen in the gas tank and all my gas lines are new stainless steel with no kinks. I bought the fuel pump from Chevy Duty. Where did you guys get your fuel pumps? Any brand better than others?

It does have the classic symptoms of fuel starvation (vapor lock, plugged line, failing pump). The next time it stalls, pull the top of the air cleaner & work the accelerator pump. If you don't get a strong stream it would indicate a fuel supply issue.

did this problem just pop up at once

I haven't had the dual setup that long. This never happened with the single carb original setup. Since I installed the dual setup, I've only been driving the truck around town. It wasn't until recently that I took it out on the highway and about 2 or 3 miles after hitting a speed over 50 to 60 mph did this begin to happen.

Bobzhog,I agree with all here,fuel problem.I had a Chev van for 28 yrs.Every year, what you discribe would happen.The filter in the Q-jet would plug up.Idled fine and speeds to 40mph then it would stall.Steep hills caused problems too.The fuel pump just can't get enough fuel to the carbs.Take the filter out and try it.

Do ya have another (Known good)coil you could swap in to rule out the coil? I have had several issues with coils on cars and on my Harleys reacting just like you have described. Chased the fuel system all day once on the Harley. Had that carb apart about 7 times that day. Turned out when i read out the coil it read good, however at speed, when it would heat up it would break down and stop. Just Two cents worth. Have a fun day.
Slider

Make sure the tank is vented. Try loosening the cap a bit. It really shouldn't be using to much more fuel then the single carburator if its set up right. Each carb should be delivering about 1/2 of what the engine needs. You can also try a fuel gauge hooked right at the carb. with flexible hose so you can see it from the drivers seat. Don't run it in the cab! put it under the wiper arm or someplace like that. Its hard to believe a coil would cool off fast enough to restart right away, sure sounds like a fuel flow problem. Joe

If you are sure the fuel isn't a problem, I'd check the coil too. When it gets hot enough, it expands creating a fault.

Let us know what you find.

Thanks for all of your help. I'll check out all of the suggested items and I'll let you know where the gremlin was (if I find the little bugger).

It,s hard to tell if one brand of pump is better than another but sometimes they have sat around a long time & can get stale. Some of the materials used years ago won,t stand the chemicals in todays gas. You can run a pressure test & volumn test on it. If all else fails I would try a new pump.

nother thing that can happen is the pump actuator gets worn enuff that it doesn't get a full stroke, so while it still works, it might not be moving as much volume - I had that situation with a stock 235 that showed up only when going up a slight grade

Bill

I would check that plumbing and linkage between those carbs. It sounds like the second carb is starving for fuel as the accelerator is advanced.

The carbs combined use about the same amount of fuel as a single carb.With about 1/2 the fuel going to each you would not see a noticable differance in performance until you exceeded the low idle or slow driving stage.

As you depress the accelerator the carbs call for fuel as the floats drop in relation to the amount of fuel you are dumping.

A common problem is a blockage between the carbs sometimes but not always related to a "softened rubber hose" that will close off as it gets hot.

A second common problem is improper linkage adjustment between the two carbs.One dual carb configuration is of the progessive type where the second carb is not dumping fuel at the same rate and time as the first carb but increases as the demand is put on it.If this is the setup you have you might need to change the linkage so that both carbs are dumping simultaneously.

Another possible problem is a malfuctioning choke.It could be that the choke is being closed from iterference of a linkage rod or other cause.Just another area I would check.

Hobert

The next time it happens try removing the gas fill cap to see if you have a vaccum in the tank, if you do the vent in the tank is blocked.

I had a problem with the same symptoms you mentioned several years ago. I went through the fuel and ignition system several times, and I still got stranded. Finally found the problem.

I had installed a new wiring harness in the truck. It came equipped with a neutral safety switch that was bipassed. The plug for the neutral safety switch was close to a clip on the firewall. When I was traveling at speeds of 55 mph or going up hill the clip and harness would short out killing the ignition. Moments later it would restart as if nothing had happened. Basically the engine fan would push the wiring harness when the engine was revving. It would short out, sputter, and or die. As the engine speed went down so did the force of push from the fan, and the harness would clear itself from the short.

I agree you probably have one of the problems that have been mentioned in the previous posts, but it is possible to have another problem like mine which would give you the same symptoms.

Good Luck!
John

I had a similar problem with my 1966 C-30. The coil was bad.

Well, I changed the coil but that wasn't the problem; so I started at the gas tank and worked my way forward. I took everything apart and blew air thru the gas lines and found no blockages all the way to the carbs. I cleaned each part and put everything back together nice and tight. I took the carbs apart and found everything in good working order. So I fired it up and it ran like a top. I took it out on the highyay and ran it up to 65mph and held it there with no problems. My guess is that it was some kind of air leak (vacuum leak) in the system and I corrected it when I reassembled the system. Go figure. Thanks for all your help.

I just love a happy ending.

check out this fuel tip
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=582585-R1-048-22A.jpg

it's inside the tank and does not allow crud to enter into the fuel line.